Self compacting concrete from uncontrolled burning of rice husk and blended fine aggregate

Materials and Design 55 (2014) 410–415

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Materials and Design
journal homepage: www.elsevier.com/locate/matdes

Self compacting concrete from uncontrolled burning of rice husk and
blended fine aggregate
M.E. Rahman a,⇑, A.S. Muntohar b, V. Pakrashi c, B.H. Nagaratnam a, D. Sujan a
a

School of Engineering and Science, Curtin University Sarawak, Malaysia
Department of Civil Engineering, Universitas Muhammadiyah Yogyakarta, Indonesia
c
School of Engineering, University College Cork, Cork, Ireland
b

a r t i c l e

i n f o

Article history:
Received 3 June 2013
Accepted 2 October 2013
Available online 10 October 2013
Keywords:
Rice husk ash
Self compacting concrete
Sustainability
Fresh state properties
Hardened state properties
Uncontrolled burning

a b s t r a c t
This paper presents an experimental study on the development of normal strength Self compacting concrete (SCC) from uncontrolled burning of rice husk ash (RHA) as a partial replacement to cement and
blended fine aggregate whilst maintaining satisfactory properties of SCC. Experiments on the fresh and
hardened state properties have been carried out on RHA based SCC from uncontrolled burning. The dosages of RHA are limited to 0%, 20%, 30% and 40% by mass of the total cementitious material in the concrete. The experiments on fresh state properties investigate the filling ability, the passing ability and
the segregation resistance of concrete. The experiments on hardened state properties investigate the
compressive and the splitting tensile strengths. The water absorption level of the concrete with changing
RHA levels has also been monitored. The experimental studies indicate that RHA based SCC developed

from uncontrolled burning has a significant potential for use when normal strength is desired.
Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction
Concrete is one of the most important materials for a very wide
range of construction work. Generally, concrete is compacted by a
vibrator or a steel bar after placing it inside the formwork to remove the entrapped air and it becomes a dense and homogeneous
material. Compaction is very important to produce good concrete
with desired strength and durability.
Self compacting concrete (SCC) is competent to flow, fill all
areas and corners of the formwork even in the presence of congested reinforcement. It compacts under its own weight without
segregation and bleeding and does not require any type of internal
or external vibrator. Self compacting concrete must satisfy three
fresh concrete properties related to the filling ability, the passing
ability and the adequate segregation resistance [1–3].
The prototype of SCC was first developed in Japan in 1988 in order to make sure durable and safe concrete structures by changing
the concept of concrete production and construction process. Significant research and development work into SCC are now being
conducted nearly all over the world [4–6]. SCC seems to have a
number of benefits in terms of economical, environmental,
mechanical strength and durability aspects over Normally Vibrated

Concrete (NVC) construction. As SCC does not require internal or

⇑ Corresponding author. Address: CDT 250 98009 Miri, Sarawak, Malaysia.
Tel.: +60 85 443939x3816.
E-mail address: merahman@curtin.edu.my (M.E. Rahman).
0261-3069/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.matdes.2013.10.007

external compaction, it reduces the segregation of coarse aggregate
from cement paste leading to less porous zones between aggregate
and cement paste. This reduction in porous zones may be related to
durability properties [3,4].
SCC requires a significant decrease of coarse aggregate and an
increase of cement content to maintain its fresh state properties
and homogeneity. High cement content generally increases overall
concrete production cost and also generates high heat during the
chemical reactions as well as increasing creep and shrinkage problems. Consequently, significant quantities of pozzolanic material
including Fly Ash (FA), rice husk ash (RHA), silica fume, Ground
Granulated Blastfurnace Slag (GGBS), etc. are frequently used to replace cement to improve the fresh state properties of concrete, to
control the generation of heat and to reduce the creep and shrinkage problems [4,5].

An increasing focus of the society towards sustainability has led
to a significant increase in the use of different types of waste materials including RHA, tires, Oil Palm Shell (OPS) and FA. Intelligent
reuse of materials is directly related to the necessity arising from
the environmental effects of waste. The reuse of waste materials
in concrete is an attempt to address a part of these problems by
introducing sustainable materials in the construction industry.
Concrete is the second most used material in the construction
industry after water. As a result, the environmental impact, including the carbon footprint of concrete, is severe.
RHA, a by-product of paddy, can be abundantly found over a
very large region of the world and is a contributor to air, river,

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M.E. Rahman et al. / Materials and Design 55 (2014) 410–415

sea and groundwater pollution. Reuse of RHA in concrete attempts
to address a part of the environmental problems. To establish the
credibility of the use of such materials, experimental studies are
important to demonstrate the efficiency of RHA blended concrete
in terms of a number of traditional performance measures of standard concrete in terms of construction usage. Consequently, it is

very important to study the physical and chemical properties of
RHA and fresh state properties and hardened state properties of
RHA based self compacting concrete extensively.
Diverse studies have been carried out on high strength conventional SCC and FA based SCC in both fresh and hardened states and
a limited number of studies also exist on RHA based normal
strength SCC. Fresh state properties of RHA based SCC along with
cost analysis have been carried out before [3] where the dosage
of RHA was limited to 5 10% by mass of the total cementitious
material. RHA based SCC was observed to be more cost effective
than Ordinary Portland Cement (OPC) based SCC. Mechanical properties of RHA based SCC have also been investigated [2] where the
dosage of RHA was limited to 10 20% by mass of the total cementitious material. It was found that the RHA based SCC yielded higher results than the OPC based self compacted concrete in terms of
strength at an age of 60 days. Durability performance of SCC has
been investigated by researchers as well [7] and it has been reported that the porosity of SCC is generally lower than that of normal concrete and hence improved resistance to corrosion, freeze
thaw cycles and sulphate attack. Hardened state properties of
RHA based SCC have been studied [8] where the dosage of RHA
is limited to 0 30% by mass of the total cementitious material. It
was found that the hardened state properties improved with the
increasing of RHA content. Some investigations have been reported
relating to the increase of strength and durability properties of
concrete through the use of RHA [9–14].

The availability of a significant amount of RHA is through
uncontrolled burning. Considering the fact that a very significant
amount of concrete construction in the developing regions around
the world is associated with the use of normal strength concrete,
there seems to be a potential of using RHA from uncontrolled burning to produce normal strength concrete with adequate fresh and
hardened state properties. There does not seem to be extensive research work present on RHA based normal strength SCC from
uncontrolled burning. A significant amount of RHA from uncontrolled burning is generated every year in many developing countries. Such RHA contains around 90% SiO2 and due to this high
percentage of SiO2 in RHA, it works as a pozzolanic material. Therefore it is very important to utilize in concrete and also to study RHA
based normal strength self compacting concrete by examining its
hardened state properties. The uses of normal strength concrete
in Malaysia and in many developing nations associate with a very
high share of all of the concrete construction. The application of
uncontrolled burning RHA as pozzolanic material in normal
strength SCC in Malaysian construction industry and similar developing nations is not usual and there is a general lack of technical
knowledge and guidance in this regard.
These paper present experimental studies on RHA based normal
strength SCC from uncontrolled burning with blended fine aggregates in relation to the adequacy of achieving fresh and hardened
state properties. Filling ability, passing ability and segregation
resistance were tested for fresh state while the compressive and
the splitting tensile strength were tested for hardened state. Additionally, a water absorption test and a comparison with FA based

SCC are carried out in this paper with respect to RHA based SCC
from uncontrolled burning. The study demonstrates the possibility
of use of RHA based SCC from uncontrolled burning as a sustainable building method for the development of normal strength
concrete.

2. Details on materials for testing
2.1. Cement
Ordinary Portland Cement (OPC) grade 42.5 based on ASTM:
C150/C150 M-12 was used in the concrete as cementitious material. The density of the cement is 2950 kg/m3.
2.2. RHA
RHA obtained through uncontrolled burning was used in this
study. The RHA was collected from a village (Kota-Kinabalo) in Sabah, Malaysia. The RHA was sieved by a 75 lm sieve to remove
large particles and was then grinded to obtain fine powder. The
chemical composition of the RHA was determined using XRF
(X-ray Fluorescence). The results of the chemical composition of
cement are presented in Table 1. The amount of SiO2 in the RHA
is observed to be 94.8%.
2.3. Coarse aggregate
10 mm nominal size crushed quartzite was used as the coarse
aggregate in this research. The coarse aggregate was composed of

particles within the range of 5 –10 mm. Sieve analysis of a
2000 g sample indicated that the entire sample (100%) passed
through a 9.5 mm sieve while only 5% passed a 4.75 mm sieve
(i.e. 95% retained on 4.75 mm sieve). This conforms with the
10 mm single sized aggregate requirements in AS: 2758.1 [15].
The gradation of coarse aggregate is presented in Table 2.
2.4. Fine aggregate
AS: 2758.1 [15] categorize aggregates with particles finer than
4.75 mm as fine aggregates (FA) for concrete mix design. In this research programme two categories of fine aggregates was used. One
category was chosen such that nominal size was 4.75 mm while all
the particles were coarser than 600 lm (crushed quartzite). The
other category had a nominal size of 600 lm (uncrushed river
sand) while sieve analysis indicated the presence of even microfines to a small extent (particles of size less than 75 lm). The gradations of the two categories chosen as fine aggregates of both
types are presented in Table 3 and Table 4 respectively.
The fineness modulus of river sand is rather small (1.32), indicating a very fine overall particle size. Very often, the desired value
for fine aggregates is 2.5 or above. Hence it is necessary to use a
coarser fine aggregate in the mix. The fineness modulus of crushed
quartzite is 4.29. The aggregate characteristics summary is presented in Table 5.
2.5. Admixture
The super-plasticizer used in this research was supplied by Sika

Kimia Sdn Bhd. The trade name of the high range water reducing

Table 1
Chemical composition of cement, RHA.
Compound

Cement (%)

RHA (%)

SiO2
CaO
Fe2O3
K2O
TiO2
MnO
CuO

20
63.2

3.3
N.A
N.A
N.A
N.A

94.8
1.41
1.61
1.33
0.17
0.28
0.04

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M.E. Rahman et al. / Materials and Design 55 (2014) 410–415

coarse aggregate was limited to 10 mm. The mix proportions of
RHA based SCC are summarized in Table 6.

Table 2
Coarse aggregate (CA) gradation.
Sieve size (mm)

% Finer

AS 2758.1 requirements

9.5
4.75
2.36

100
5
0

85–100
0–20
0–5

3.2. Sample preparation

Table 3
River sand gradation.
Sieve size (lm)

% Finer

AS 2758.1 requirements

600
300
150

100
58
10

15–100
5–50
0–20

Table 4
Crushed quartzite gradation.
Sieve size

% Finer

AS 2758.1 requirements

4.75 mm
2.36 mm
1.18 mm
600 lm

99
50
20
2

90–100
60–100
30–100
15–80

(up to 30% depending on dosage) admixture is SikamentÒ-NN and
conforms to the requirements of ASTM C494/C494 M-13 while the
chemical base of the dark brown liquid is Naphthalene Formaldehyde Sulphonate. The use of admixture is advocated along with
the application of the use of RHA from uncontrolled burning to enhance the workability and the reduction of water requirement.
Such admixtures used during normal production of concrete and
consequently the use of RHA can be effective in reducing the cost.

3. Details of experimentation
3.1. Mix proportions
Four concrete mixes were designed and the dosage of RHA are
limited to 0%, 20%, 30% and 40% respectively by the mass of the total cementitious material. Crushed quartzite was mixed with river
sand to increase the fineness modulus of fine aggregates. The fineness modulus of river sand was 1.32 and the maximum size of the

The mixer used was a 0.5 m3 capacity forced action cylindrical
pan mixer with a vertical axis of rotation. For optimal mixing outcomes a specific procedure was chosen from a number of different
methods of mixing. The procedure most suited to the experiments
involved putting all the aggregates into the pan and running the
mixer for around 1 min. Following this run, RHA powder was
added and the mixer was run for approximately another 1 min.
Next, about 60% of the required water was added slowly (poured
towards, but not too close to the outer wall of the pan) and mixer
was run again for around 1–1.5 min. Once this mixing was carried
out, 30% of the water and 90% of the super-plasticizer was mixed in
a bucket and then added slowly to the pan before running it for
about 3–3.5 min. The super-plasticizer was found out to be most
effective when added with water. The consistency and the flow
of the resulting mixes were observed and the remaining 10% of
water and 10% of super-plasticizer (mixed together) were used to
adjust the mix. This step was found out to be especially helpful
due to the changes in water and super plasticizer demand as
RHA content was increased. The step took about 40–50 s. The
resulting mixture was then allowed to rest for not less than
2.5 min (for air dissipation), and remixed for 20–30 s, after which
all the fresh state tests were carried out. With increasing the
RHA content in the mix, the need to follow this procedure was
obvious since the mixture tended to be more viscous and sudden
addition of water lead to complete failures in terms of achieving
the desired SCC.
3.3. Testing of samples
3.3.1. Fresh state properties
SCC must satisfy three fresh concrete properties including the
filling ability, the passing ability and the adequate segregation
resistance. For determining the filling ability, slump flow and
V-funnel tests were carried out. The passing ability was
determined through J-ring test while the segregation resistance
was determined through sieve segregation tests. The performance
criteria for fresh state concrete properties of SCC are presented in
Table 7 [4,5,8].
The slump flow indicates the ability to completely fill all areas
and corners of the formwork into which it is placed. It measures
the average diameter from two perpendicular directions of the
mass of the concrete after taking out the standard slump cone.

Table 5
Aggregate characteristics summary.

Fine aggregate
Coarse aggregate

Material type

Size range

Fineness modulus

Water absorption (%)

Specific gravity

Uncrushed river sand
Crushed quartzite
Crushed quartzite

0.0–600 lm
600 lm to 5.0 mm
5.0–10.0 mm

1.32 (low)
4.29 (high)

1.10
1.30
1.40

2.64
2.67
2.62

Table 6
Mix proportions of RHA based SCC.
Materials

Cement (kg/m3)

RHA (kg/m3)

Water (kg/m3)

w/p

sp%

River sand (kg/m3)

Crushed quartzite (kg/m3)

Coarse aggregate (kg/m3)

Mix
Mix
Mix
Mix

540
400
350
300

0
100
150
200

205
250
250
250

0.38
0.5
0.5
0.5

1.8
3.5
3.5
3.5

230
150
150
94

630
700
700
756

690
700
700
700

1
2
3
4

M.E. Rahman et al. / Materials and Design 55 (2014) 410–415
Table 7
Performance criteria for fresh state SCC [4,5,8].
Test method

Property

Criterion

Slump flow
V-funnel
J-ring
Sieve segregation

Filling ability
Filling ability
Passing ability
Segregation resistance

550–850 mm
6–12 s
0–10 mm
618%

Fig. 1. J-Ring sample.

V-funnel test was carried out to determine the stability of SCC
mixes which determine the flow time. J-ring test (Fig. 1) was carried out to determine passing ability of the SCC through congested
reinforcement without separation of the constituents or blocking.
This test measures the difference in height between the concrete
inside the bars and that just outside the bars. Sieve segregation test
was carried out to determine the resistance to segregation of SCC
to retain the coarse components of the mix in suspension in order
to maintain a homogeneous material.
3.3.2. Hardened state properties
The hardened state properties of the concrete include strengths
in compression and tension properties. Cylindrical specimens were
tested to failure to determine hardened state properties like compressive strength and splitting tensile strength at 3, 7, and 28 days
respectively using Universal Testing Machine. Adequate strength in
compression and tension establishes the uses of RHA based SCC
from uncontrolled burning for the production of normal strength
concrete.
4. Results and discussions

413

flow diameter is 630 mm, V-funnel flow time is 5.9 s, the difference
in height in J-ring is 5.2 m and the segregation ratio is 8.2%. For Mix
2, the slump flow diameter is 660 mm, V-funnel flow time is 6.6 s,
the difference in height in J-ring is 3.7 mm and the segregation ratio is 0.04%.
For Mix 3, the slump flow diameter is 670 mm, V-funnel flow
time is 6.3 s, the difference in height in J-ring is 3.5 mm and the
segregation ratio is 0.09%. For Mix 4, the slump flow diameter is
580 mm, V-funnel flow time is 7.0 s, the difference in height in Jring is 4.4 mm and the segregation ratio is 0.2%.
Slump flow test was carried out to investigate the filling ability
of normal strength SCC. The standard range of slump flow diameter
is 550–850 mm. If the slump flow (SF) value is higher than
750 mm, the viscosity will be lower and the greater its ability to fill
formwork under its own weight however concrete might segregate. If the slump flow (SF) value is lower than 500 mm, the viscosity will be higher and greater its chance to make blockage in
congested reinforcement. All the results from this study fall within
the middle range, which indicates an excellent filling ability of normal strength SCC.
V-funnel test was also carried out in addition to the slump flow
test to investigate the filling ability of normal strength SCC. The
standard range of V-funnel flow time is 6–12 s as per EFNARC
[4]. This test measures the ease of flow of the concrete. The longer
flow times indicate lower flowability and shorter flow times indicate greater flowability. The results from this study are higher than
the minimum standard value of 6 s and lower than the maximum
standard value of 10 s.
J-ring test was carried out to investigate passing ability of the
normal strength SCC. This test measures the difference in height
between the concrete inside the bars and that just outside the bars.
The standard range of difference in concrete height between the
concrete inside and outside the bars is 0–10 mm. The greater the
difference in height, the passing ability of the concrete is low and
the lower the difference in height; the passing ability of the concrete is high. All the results from this research work are less than
10, which indicate a good passing ability of RHA based normal
strength SCC.
The sieve segregation resistance test was carried out to investigate the resistance of normal strength self-compacting concrete to
segregation. The standard limiting value for sieve segregation
resistance test is less than 18%. As per EFNAC, if the result is higher
than 15%, the viscosity will be lower, the concrete might segregate.
The results from this research work are less than 15%, which indicate that RHA based normal strength SCC is a good resistance to
segregation [4,5].
It is noted from these experiments on the fresh state properties
that the RHA based SCC from uncontrolled burning satisfies all the
criteria of the fresh state properties of SCC including filling ability,
passing ability and segregation resistance. Consequently, the material has good potential as a cement replacement in the production
of SCC.

4.1. Fresh state properties
4.2. Hardened state properties
The results of the slump flow, V-funnel, J-ring and Sieve segregation test for the fresh state properties of RHA based self compacting concrete are presented in Table 8. For Mix 1, the slump

Table 8
Fresh state properties of rha based SCC.
Test method

Mix 1

Mix 2

Mix 3

Mix 4

Slump flow (mm)
V-funnel (s)
J-ring (mm)
Sieve segregation (%)

630
5.9
5.2
8.2

660
6.6
3.7
0.04

670
6.3
3.5
0.09

580
7
4.4
0.2

4.2.1. Compressive strength
The compressive strength of RHA based SCC are evaluated at 3,
7 and 28 days and the results are presented in Table 9. The percentage of RHA content in the Mix1, Mix2, Mix3 and Mix4 are 0, 20, 30
and 40 respectively. It can be seen from the Table 9 that the compressive strength decreased with increasing of RHA content. Previous studies [2,9,16] showed that the 28 days compressive strength
decreased with increasing of RHA content. It is due to the fact that
the amount of RHA present in the mix is higher than the amount
required and due to the leached out extra silica. This extra silica replaces part of the cementitious material and does not contribute to

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M.E. Rahman et al. / Materials and Design 55 (2014) 410–415

Table 9
Compressive strength of SCC.

Table 10
Splitting tensile strength of SCC.

Compressive strength (MPa)
RHA based SCC

Splitting tensile strength (MPa)
RHA based SCC

Days

Mix 1

Mix 2

Mix 3

Mix 4

Days

Mix 1

Mix 2

Mix 3

Mix 4

3
7
28

28.2
32.8
48.5

26.1
37.2
42.9

23.4
35.1
40.9

20.9
28.1
33.5

28

5.1

5.1

4.3

2.8

Compressive Strength, MPa

50

Mix1, RHA 0%
Mix3, RHA 30%
Mix2, Fly Ash 20%
Mix4, Fly Ash 40%]

45

Spliting Tensile Strength, MPa

5.5

Mix2, RHA 20%
Mix4, RHA 40%
Mix3, Fly Ash 30%

40
35
30
25

RHA
Fly Ash

5

Felekoglu et al (19)
Shafigh et al (20)

4.5

Browers and Radix (21)
Slate et al (22)

4
3.5
3
2.5
2

20
1.5
20

15
0

5

10

15

20

25

25

Age, Days

30

35

40

45

50

55

Compressive Strength, MPa

30

Fig. 3. Relationship between 28-days compressive and splitting tensile strength.

Fig. 2. Compressive strength of SCC mixes.

compressive strength [16]. Compressive strength of RHA based SCC
along with the results obtained from similar studies carried out on
fly ash based SCC are presented in Fig. 2. It can also be observed
from Fig. 2 that the compressive strength decreased with increasing of fly ash content. Studies [17] also showed that the compressive strength decreased with increasing of FA content. At an early
stage, the rate of gain of strength of RHA based SCC was higher
due to presence of higher percentage of silica in RHA. The higher
percentage of silica helps the pozzolanic reactions occur at early
ages [18]. However, the rate of gain of strength was lower after
7 days. In general RHA based SCC yielded higher strength than similar studies carried out on FA results. However, the 28 day
strengths of Mix2 (Fly Ash) are higher than RHA based SCC, an
obvious reason of which is not apparent. Generally, the strength
gain of RHA is consistently more rapid than the FA based SCC
and the maximum compressive strength is reached quite early.

4.2.2. Splitting tensile strength
The splitting tensile strength test results of RHA based SCC are
presented in Table 10. The percentage of RHA content in the Mix1,
Mix2, Mix3 and Mix4 are 0, 20, 30 and 40 respectively. It can be
seen from Table 10 that the splitting tensile strength decreased
the same as the compressive strength with the increasing of RHA
content. This relationship between the compressive strength and
the splitting tensile strength of RHA based SCC is presented in
Fig. 3. The findings correspond to some previous studies [19–22].
The correlation between the splitting tensile strength and compressive strength are presented in Table 11. It can be seen from
Fig. 3 that the splitting tensile strength increases with increasing
the compressive strength. The splitting tensile strength of SCC
based on RHA was 8–12% of compressive strength. It can also be
observed in Fig. 3 that the splitting tensile strength of SCC are higher than the normal vibrating concrete due to uniform compaction
of SCC under its own weight without any types of internal and
external vibrator and without segregation and bleeding. Felekoglu
et al. [19] also found that the splitting tensile strength of SCC is
higher than the normal vibrating concrete.

Table 11
Equations for splitting tensile strength.
0.0007(fc)2.3437
0.676(fc)0.4759
0.4887(fc)0.5
0.43(fc)0..6
1 N/mm2 + 0.05 fc
0.51(fc)0..5

RHA based SCC [experimental]
Studies based on FA
Felekoglu et al. model [21]
Shafigh et al. model [22]
NEN 6722 model [23]
Slate et al. model [24]

4.2.3. Water absorption test
The water absorption test results of RHA based SCC are presented in Table 12. The percentage of RHA content in the Mix1,
Mix2, Mix3 and Mix4 are 0, 20, 30 and 40 respectively. It can be
seen from Table 12 that the water absorption of the SCC increased
with the increasing of the content of RHA. Previous studies [23]
showed that the water absorption level increased with increasing
of RHA content in concrete. RHA is finer than cement. The total binder surface area increased with increasing the RHA content in SCC
and thus the water absorption level of concrete also increased [23].
4.3. Materials and carbon footprint
Significant amounts of virgin materials including limestone and
clay besides energy are consumed to produce cement and 1.5 ton
of virgin materials are needed to produce one ton of cement [24].
Cement production industries are liable for more or less 7% of
the world0 s carbon dioxide discharge and to produce one tone of
cement approximately one ton of CO2 is released in the atmosphere [24,25]. RHA is a by-product of paddy which can be abundantly found over a very large region of the world and is a

Table 12
Water absorption (%).
RHA based SCC
Days

Mix 1

Mix 2

Mix 3

Mix 4

28

6.2

7.7

8.9

10.5

M.E. Rahman et al. / Materials and Design 55 (2014) 410–415

contributor to air, river, sea and groundwater pollution. This study
shows that RHA has good potential as a cement replacement up to
40% in normal strength self compacting concrete production. Every
year significant amount RHA from uncontrolled burning is produced by villagers in developing countries. The reuse of waste
materials in concrete is an attempt to address a part of these problems by introducing sustainable materials in the construction
industry and consequently reduce carbon footprint.

415

tion between tensile strength and compressive strength of
concrete.
 The splitting tensile strength of SCC is higher than the normal
vibrating concrete due to better homogeneous mixture of SCC.
 The water absorption level increased with increasing of RHA
content as it is hygroscopic in nature.

Acknowledgements
4.4. Discussion on durability aspects
Care should be taken in relation to proper curing of this concrete since poor curing affects durability more significantly than
an Ordinary Portland Cement (OPC) concrete of similar strength.
The water permeability of concrete with RHA will eventually be
lower than an equivalent OPC due to continued hydration beyond
28 days. The porosity will also be lower for correctly manufactured
concrete due to precipitation of gel products in pores and this will
be more effective for elevated curing temperatures. Resistance to
chloride ingress will be increased with increased RHA content in
concrete. This reduction in the average pore diameter of cement
paste caused by the incorporation of rice husk ash in the mix effectively reduces the pore sizes, permeability and diffusivity of chloride ions in concrete [11]. The carbonation of concrete with RHA
is expected to be eventually at the same level as of OPC concrete,
although the early rate of carbonation can be higher for concrete
with RHA. Higher levels of RHA can also aid in sulphate resistance.
Performance against freeze–thaw effect can be inferior to OPC but
this may be improved through air entrainment and good curing.

5. Conclusions
In general, RHA has good potential as a cement replacement in
normal strength self compacting concrete production and can even
be used for construction of low-cost housing project. Simultaneously, the use of RHA also reduces waste materials. The following observations and conclusions can be made on the basis of the
current experimental results:
 Concrete blended with RHA obtained from uncontrolled burning is able to produce normal strength self compacting concrete
with incorporating up to 40% RHA as supplementary of cementing material and blended fine aggregate without compromising
the fresh state properties.
 The ranges of slump flow diameter for all the mixes are 580 to
670 mm indicating an excellent filling ability of SCC.
 The V-funnel flow time ranges are 6.3 to 7 s indicating also an
excellent filling ability of SCC.
 The ranges of difference in height between the concrete inside
the bars and that just outside the bars are 3.5 to 4.4 mm indicating a good passing ability of SCC.
 The sieve segregation resistance value falls in the range of 0.04
to 0.2% indicating a good resistance to segregation of SCC.
 Compressive strength and splitting tensile strength decreased
with increasing of RHA content. It is due to the fact that the
amount of RHA present in the mix is higher than the amount
required and due to the leached out extra silica. This extra silica
replaces part of the cementitious material and does not contribute to compressive strength.
 With increasing the RHA content in the mix, the mixture tended
to be more viscous and especially sudden addition of water lead
to complete failures in terms of achieving the desired SCC.
 The splitting tensile strength of SCC based on RHA was 8–12% of
compressive strength respectively which satisfies the correla-

The first Author is grateful to the R&D Department, Curtin University Sarawak for financial support to conduct this research work
under CSRF scheme (Approval No: 2011-14-AG-ZZ). The first
author would also like to thank Mr. Ung Chai & Mr. Ahmed Faheem
for their support in the experimental works.
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